bundle.add: fix theme being persisted twice
bundle.add: fix theme being persisted twice

`omf theme` was persisting the installed theme twice, one time on
`omf.install` and other time on `omf.bundle.add`.

MaicoTimmerman/oh-my-fish,jeremiejig/oh-my-fish,bsott/oh-my-fish,nwykes/oh-my-fish,oranja/oh-my-fish,nwykes/oh-my-fish,oh-my-fish/oh-my-fish,wangyung/oh-my-fish,hfs/oh-my-fish,bobthecow/oh-my-fish,lfiolhais/oh-my-fish,eugenesvk/oh-my-fish,wfscheper/oh-my-fish,hfs/oh-my-fish,scorphus/oh-my-fish,wfscheper/oh-my-fish,jeremiejig/oh-my-fish,bsott/oh-my-fish,oh-my-fish/oh-my-fish,lfiolhais/oh-my-fish,sheldon/oh-my-fish,wangyung/oh-my-fish,eugenesvk/oh-my-fish,oranja/oh-my-fish,MaicoTimmerman/oh-my-fish,scorphus/oh-my-fish,Pyppe/oh-my-fish